1. Field of the Invention
This invention relates to an improvement of method and apparatus for transferring and fixing a toner image by means of an intermediate transfer member.
2. Description of the Prior Art
Generally in a picture recording apparatus provided with an intermediate transfer member, a toner image on a toner image retainer which is formed from having a latent image developed by a developing toner is transferred onto the intermediate transfer member in endless belt or roll, and then the toner image once transferred onto the intermediate transfer member is retransferred further onto a transfer material or transfer paper or the like and fixed to a picture. According to such apparatus, not only a high grade of picture can be obtained but also a system to record a multitude of the same pictures by utilizing the latent image once formed more than one time through repeating development and transfer, or the so-called retention system can be introduced, thus facilitating a high-speed operation for picture recording. In addition, the image can be transferred onto a transfer material consisting of an ordinary paper even from using a single component conductive toner as a developing toner, therefore a developing system can be simplified and a picture quality can be improved to an advantage.
Then, various severe conditions may prevail for the concurrence of fixation with transferring the toner image on the intermediate transfer member onto the transfer material, therefore it is considerably difficult to attain transfer and fixation of a quality toner image at the same time.
As described in Japanese Patent Publication No. 41,679/1971, for example, hitherto known is such a means as will heat a transfer material without heating a toner of the toner image on an intermediate transfer member and thus transfer and fix the toner image with a heat of the transfer material.
This means is preferable as far as the intermediate transfer member will be kept from overheating and hence a thermal influence will be prevented from exerting on a toner image retainer, however, an availability of the heat is low, and thus a considerable quantity of thermal energy must be applied onto the transfer material consisting of an ordinary paper. Moreover, a thermal energy to be applied on the transfer material is different in quantity according to the kind of transfer material normally consisting of a paper, the thermal energy is necessary in large quantities for the transfer material consisting of a paper weighty or porous accordingly, the thermal energy equivalent thereto which is given to the transfer material consisting of a paper light or thin may invite overheating to a deformation or a burnt hole of the transfer material in consequence, and therefore the thermal energy to feed must be adjusted according to the kind of transfer material to attain transfer and fixation in good condition. Further, when transfer and fixation of the toner image are carried out at high speed, a large quantity of the thermal energy will have to be given to the transfer material further more, a consumption energy increases as a result, and when the transfer material is not carried smoothly to cause a jam, there may result a firing in most cases.
As described in Japanese Patent Laid Open No. 78,559/1974, on the other hand, such means is also well known as will transfer a toner image on the intermediate transfer member onto the transfer material to fixation by heating a toner of the toner image on the intermediate transfer member up to the fusion temperature without heating the transfer material
However, the transfer material deprives the toner much of heat in this means, therefore a fluidity of the toner on the side in contact with the transfer material deteriorates to make it unlikely that the image can be fixed securely, and thus the intermediate transfer member must be heated considerably high in practice. The toner image retainer is unavoidably heated through the intermediate transfer member as a result, and where the toner image retainer is an electrophotographic sensitive member, a density of the picture image deteriorates due to initial potential drop, a material component of the intermediate transfer member sticks to the surface of the toner image retainer to cause fogging, a deterioration of the intermediate transfer member is accelerated, and thus a durability cannot be secured.
To settle such problem, it is conceivable that the intermediate transfer member be cooled down in a moving passage domain after transfer and fixation, however, energy will be consumed furthermore for forced cooling, and the moving passage required for coming in contact with the toner image retainer must be extended further for natural cooling, which may enlarge the apparatus in construction accordingly.
As already described, the toner at the time of transfer and fixation has the side in contact with the transfer material cooled down antecedently to deteriorate in the fluidity, therefore the toner does not transit completely to the transfer material and remains partly on the intermediate transfer member as sticking to stain the toner image retainer and also to give rise to an offset phenomenon.